Tournaisian (Early Carboniferous) foraminifers of the Kuznetsk Basin (South-West Siberia, Russia)

Abstract

The Taidon and Fomin formations of the Kuznetsk Basin (SW Siberia, Russia) were sampled in three sections, Old Belovo quarry, Artyshta village and Starobachaty village. The carbonate beds revealed microfacies of bioclastic wackestone and packstone, deposited in the distal parts of inner ramps and the proximal parts of mid ramps. Relatively rare plurilocular foraminifers occur in bioclastic neomicrosparitized wackestone deposited in the shallower parts of the carbonate ramp. The other microfacies only contain the bilocular foraminifer genus Earlandia. The plurilocular foraminifers permit the dating of the lower part of the Taidon Formation and the distinction of a biozone characterized by Tuberendothyra, Pseudoplanoendothyra, and Granuliferella. This local biozone can be correlated with the MFZ4 reference-biozone established in Belgium, which is late Hastarian (i.e., latest early Tournaisian) in age. Conodonts of the upper Siphonodella crenulata Zone in the lower part of Taidon Formation are consistent with this late Hastarian age. The Fomin Formation cannot be directly dated by its foraminifers Earlandia. As it is overlain by previously dated lower Visean beds, the Fomin Formation corresponds to all or part of the entire Ivorian (i.e., late Tournaisian) and of the MFZ5 to MFZ8 biozones. The same uncertainty on the late Tournaisian age exists with the conodonts, which belong to the lower Siphonodella crenulata Zone and isosticha-upper crenulata/typicus/anchoralis-latus zones, respectively. As a taxonomical result, Septabrunsiinoidea n. superfam. is introduced, in order to explain some poorly known lineages of the Tournaisian. Palaeobiogeographically, SW Siberia is proposed as the radiation centre of the Septabrunsiinoidea during the Tournaisian, and especially during the Hastarian, and their migration centre toward three directions: North America, South China and western Tethyan areas.